JPH0827983B2 - Optical information recording medium - Google Patents

Abstract

An optical information recording medium comprising a light transmitting substrate, a light absorptive layer containing at least one light absorbing substance formed on the substrate and a light reflective layer made of a metal film formed on the light absorptive layer, wherein an optical parameter represented by rho = nabsdabs/ lambda wherein nabs is the real part of the complex refractive index of the light absorptive layer, dabs is the average thickness of the light absorptive layer and lambda is the wavelength of a reading laser beam, is 0.6< rho <1.6.

Description

The present invention relates to an optical information recording medium having at least a light absorbing layer and a light reflecting layer on a transparent substrate.

[Prior Art] An optical information recording medium capable of recording data by irradiating a laser beam has a recording layer including a metal layer such as Te, Bi and Mn and a dye layer such as cyanine, merocyanine and phthalocyanine. The pits are formed and the data is recorded by means of deforming, sublimating, evaporating or modifying the recording layer by irradiating the laser beam. In an optical information recording medium having this recording layer, a void is generally provided behind the recording layer in order to facilitate deformation, sublimation, evaporation or modification of the recording layer when forming pits. . Specifically, for example, a so-called air sandwich structure, in which two substrates are stacked with a space therebetween, is used.

In this optical information recording medium, the translucent substrate 1 is used.
Laser light is irradiated from the side to form pits. And
When the recorded data is reproduced, the substrate 1 side is irradiated with a laser beam having a power weaker than that at the time of recording, and a signal is read due to a difference in reflected light between the pit and other portions.

On the other hand, a so-called ROM type optical information recording medium in which data is recorded in advance and the data cannot be written or erased thereafter has already been widely put to practical use in the information processing and audio departments. This kind of optical information recording medium does not have a recording layer as described above, and pits for reproducing recorded data are formed beforehand on a polycarbonate substrate by means of a press or the like, and Au, Ag A light reflecting layer made of a metal film such as Cu, Al or the like is formed and further covered with a protective layer.

The most typical of these ROM type optical information recording media is a compact disc, which is widely used in the audio sector and the information processing sector, so-called CD, and the specifications of the recording and reproducing signals of this CD are the so-called CD standard. A playback device conforming to this standard is a compact disc player (CD
It is extremely widespread as a player).

[Problems to be Solved by the Invention] Since the above optical information recording medium is also a recording means that uses the same laser light as a CD, it is strongly desired that the optical information recording medium conforms to a CD that has already been widely spread.

However, the above-mentioned optical information recording medium has a recording layer not found in CD, and means for forming pits on this recording layer, not on the substrate, is used for recording. Furthermore, since the recording layer has a void layer for facilitating the formation of pits, the reproduced signal naturally differs from that of the CD. Therefore, it is difficult to satisfy the above-mentioned CD standard, which defines the standard for so-called CD. In particular, under the present circumstances, a reproduction signal conforming to the CD standard cannot be obtained due to the low reflectance of the laser light incident from the transparent substrate side.

The present invention has been made to solve the above-mentioned conventional problems, and is a CD having a high reflectance and a high degree of modulation of a reproduction signal.
An object of the present invention is to provide an optical information recording medium from which a reproduced signal conforming to the standard can be obtained.

[Means for Solving the Problems] That is, in order to achieve the above-mentioned object, the gist of the means adopted in the present invention is to provide a light-absorbing dye directly or through another layer on a substrate having a light-transmitting property. In an optical information recording medium in which a light absorbing layer including the light absorbing layer is provided, and a light reflecting layer made of a metal film is provided on the light absorbing layer directly or through another layer, the real part of the complex refractive index of the light absorbing layer ρ = n _abs d _abs / λ given by n _abs , film thickness d _abs, and reproduction light wavelength λ is 0.
6 <ρ <1.6, and the imaginary part k of the complex refractive index of the light absorption layer
_The optical information recording medium is an optical information recording medium in which _abs is k _abs <0.2.

Further, in the above case, the optical information recording medium is one in which the light absorbing layer is a cyanine dye.

In the above optical information recording medium, the cyanine dye forming the light absorbing layer is a compound represented by the following general formula.

However, A and A ′ are an atomic group forming a benzene ring or a substituted benzene ring or forming a naphthalene ring or a substituted naphthalene ring, and may be the same or different. B is pentamethine (-CH = CH-CH =
CH-CH =), each hydrogen atom may be substituted with a halogen atom, an alkyl group, an alkoxy group, a diphenylamino group or the like, and has a substituted or unsubstituted cyclic side chain extending over a plurality of carbons. May be.

R ₁ and R ₁ ′ are a substituted or unsubstituted alkyl group, alkoxy group, alkylhydroxy group, aralkyl group, alkenyl group, alkylcarboxyl group, alkylsulfonyl group or an alkylcarboxyl group bonded to an alkali metal ion or an alkyl group, or It is an alkylsulfonyl group and may be the same or different.

X ₁ ^- represents a halogen atom, perchloric acid, borofluoride hydrochloric acid, benzenesulfonic acid, toluenesulfonic acid, alkylsulfonic acid, benzenesulfonic acid, an anion such as an alkyl carboxylic acid or trifluoromethyl carboxylic acid, When R ₁ and R ₁ ′ have a group to which an alkali metal ion is bonded, X ₁ ⁻ may not be present.

[Operation] In this optical information recording medium, by irradiating the light absorbing layer with laser light, energy generated in the light absorbing layer spreads to another layer adjacent to the light absorbing layer, and a layer adjacent to the light absorbing layer, For example, the substrate or the like is locally deformed to form an optically modified portion (pit). Thus, the optically modified portion formed on the surface of the substrate or the like approximates a pit previously formed by means such as pressing.

Real part n _abs of complex refractive index and its film thickness d on a transparent substrate
ρ = n _abs d _abs / λ given by _abs and the wavelength λ of the reproduction light
According to the optical information recording medium having the light absorption layer 2 satisfying the condition of 0.6 <ρ <1.6 and having the light absorption layer 3 made of a metal film behind it, a high reflectance is obtained and the reflectance is 70%. It is possible to secure the standard characteristics defined in the CD standard as described above.

For example, FIG. 4 shows the real part n _abs of the complex index of refraction of the light absorption layer of the optical disc, the film thickness d _abs, and the wavelength λ of the reproducing light when a semiconductor laser having a wavelength λ = 780 nm is used as the reproducing light. 6 is a graph showing the relationship between given ρ = n _abs d _abs / λ and the reflectance of light incident from the substrate side.

This graph is expressed as a function in which an exponential function and a periodic function are combined, and the amplitude of the periodic function increases as ρ increases.

As can be seen from this graph, the reflectance can exceed 70% at the peak point. The amplitude of this periodic function is determined by the complex refractive index of the layers that make up the optical information recording medium, the film thickness,
It changes with those homogeneity etc. as parameters. For example,
When the refractive index of the layer on the light incident side of the light absorption layer is small, the reflectance is shifted in the direction in which the reflectance becomes high as a whole graph. Also, this graph shows k _abs , d
It is expressed by an exponential function with _abs as a parameter, and it is known that the larger the imaginary part k _abs of the complex refractive index of the light absorption layer, the larger the attenuation of the reflectance of the entire graph.

The light absorption layer is homogeneous and the real part of its complex index n _abs ,
As long as there is no non-uniform distribution in the film thickness _dabs , it is known from the simulation by the inventors of the present invention that there is no change in the period of the points showing the peaks in the above graph.

The reflectance at the bottom point of the graph can be increased by controlling the above parameter conditions depending on the conditions.However, when ρ is set near the bottom point, the degree of modulation is increased. It is difficult to obtain, and in some cases, the reflectance may be higher than that before recording. Therefore, it is desirable to set ρ near the peak point.

From the simulation results of the present inventors, 0.6 <ρ
In the range of <1.6, there are two peak points and always 0.6 <
It is in the range of ρ <1.10 and in the range of 1.10 <ρ <1.6, and it is known that a high reflectance can be obtained in them.

When 0.6 ≧ ρ, the modulation degree due to recording is smaller than the range of the present invention because the amplitude of the periodic function is small. Further, when 1.6 ≦ ρ, the film thickness becomes large, which makes it difficult to control the film thickness, which is a problem in manufacturing.

FIG. 5 shows the optical transmissivity of a light absorbing layer made of a cyanine dye in an optical disc using an Au film as a reflective layer,
Each reflectance is shown when the imaginary part k _abs is changed from a value close to 0 to 1.0 while keeping the real part of the complex index constant as n _abs = 3.2 and n _abs = 4.7. In addition,
The d _abs was set to the optimum condition within 0.6 <ρ <1.10. As can be seen from this graph, it is difficult to obtain high reflectance when k _{abs of} 70% or more is larger than 0.2.

Further, the light absorption layer made of a cyanine dye has n _abs , k
_Since it is easy to set the numerical value of _abs , a clear optically modified portion can be formed on the surface of the layer adjacent to the light absorption layer, for example, the substrate. A reproduction signal having a high degree of modulation can be obtained from the pits, and a recordable optical information recording medium compliant with the CD standard can be easily obtained, which is desirable.

[Embodiment] Next, an embodiment of the present invention will be described in detail with reference to the drawings.

An example of a schematic structure of the optical information recording medium according to the present invention,
It is shown in FIGS. In the figure, 1 is a transparent substrate, 2 is a light absorption layer formed thereon, 3
Indicates a light reflection layer formed thereon, and 4 indicates a protective layer provided on the outside thereof.

FIG. 2 shows a state before recording with laser light, and FIG. 3 shows a state after recording, that is, when the laser light 7 is converged and irradiated from the optical pickup 8 onto the light absorption layer 2. A state in which the surface is partially deformed and pits 5 are formed is schematically shown.

The transparent substrate 1 is a highly transparent material having a refractive index in the range of 1.4 to 1.6 with respect to laser light, and is made of a resin mainly having excellent impact resistance, such as a polycarbonate plate, an acrylic plate, or an epoxy plate. Although used, a glass plate or the like may be used in some cases. Further, the substrate may be coated with another layer, for example, a solvent resistant layer such as SiO ₂ or an enhancement layer.

The material used for the light absorbing layer 2 is a light absorbing organic dye, and is a polymethine dye, a triarylmethane dye, a pyrylium dye, a phenanthrene dye, a tetradehydrocholine dye, a triarylamine dye,
Examples thereof include squarylium-based dyes, croconic methine-based dyes, and merocinian-based dyes, but the invention is not limited thereto, and the effects of the present invention can be obtained as long as they are light-absorbing organic dyes. Specifically, the following are mentioned.

Polymethine dye However, in the above chemical formulas (10) to (13), A, B,
D and E represent a substituted or unsubstituted aryl group,
R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ may be the same or different and each represents a hydrogen atom, a halogen atom or an alkyl group, and Y is a 5-membered ring or 6 Represents a residue having an atomic group necessary for completing a member ring, R ₈ and R ₉ may be the same or different, and each is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group. Or an alkenyl group, Z ₁ and Z ₂ represent an atomic group necessary for completing a substituted or unsubstituted heterocycle, and Z ₃ represents a substituted or unsubstituted 5-membered ring or 6-membered ring. The above-mentioned 5-membered ring or 6-membered ring may be condensed with an aromatic ring, R ₁₀ represents a hydrogen atom or a halogen atom, and R ₁₁ and R ₁₂ represent a hydrogen atom or a halogen atom. Atom, hydroxy group, carboxyl group, alkyl group, substituted or unsubstituted aryl group, or Shows the acyloxy group, and l, m
And n is 0 or 1.

Triarylmethane dye However, in the above chemical formulas (14) and (15), R ₁ ,
R ₂ and R ₃ may be the same or different and each represents a hydrogen atom, hydroxy, a halogen atom, a C _{1 to} C ₂₀ alkyl group or —N (C _{1 to} C ₁₀ alkyl) ₂ , and l and m And n represent 0 or 1 to 9, A _r1 , A _r2 and A _r3 may be the same or different and each represents a substituted or unsubstituted aryl group, and s, t and u are 0 or 1 3 and s + t + u
= 3.

Bilium dye However, in the above chemical formulas (16) and (17), X,
X ₁ and X ₂ represent a sulfur atom, an oxygen atom or a selenium atom,
Z and Z ₁ are necessary to complete an optionally substituted pyrylium, thiopyrylium, selenapylylium, benzopyrylium, benzothiopyrylium, benzoselenapyrylium, naphthopyrylium, naphthothiopyrylium or naphthoselenapyrylium. Represents a hydrocarbon group consisting of a group of atoms, Z ₂ is optionally substituted pyran, thiopyran,
Selenapyran, benzopyran, benzothiopyran, benzoselenapyran, naphthopyran, naphthothiopyran, or a hydrocarbon group consisting of an atomic group necessary for completing naphthoselepyran, R ₁ , R ₂ , R ₃ and R ₄ are hydrogen atoms, and substituted. Or an unsubstituted alkyl group or a substituted or unsubstituted aryl group, R ₅ , R ₆ and R ₇ are a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group or a substituted or Represents an unsubstituted aralkyl group, m and l represent 1 or 2, and n represents 0, 1 or 2.

Phenanthrene dye However, in the above chemical formulas (18) and (19), R ₁ and R ₂ represent an alkyl group, and R ₃ , R ₄ and R ₅ represent a hydrogen atom, hydroxy, a halogen atom, substituted or unsubstituted alkyl, aryl, Represents an aralkyl, amino or alkoxy group, And l, m and n represent 0 or 1 to 6. Tetrahydrocholine dye However, R ₁ is alkyl, carboxyalkyl such as CO
OC ₂ H _{5 and the} like, R ₁ represents hydrogen, an alkyl group and the like, and M represents H, Ni (II), Co (II), Co (III) and the like.

Triarylamine dye However, in the above formulas (21) and (22), R _{1 to} R ₃ ,
l, m, n, Ar _{1 to} Ar ₃ , s, t and u are represented by the above chemical formula (1
This is the same as described in 4) and (15).

Examples of the counter ion for the dye cation in the above chemical formulas (10) to (22) include chloride ion, bromide ion, iodide ion, perchlorate ion, benzenesulfonate ion, p-toluenesulfonate ion, There are acid anions such as methyl sulfate ion, ethyl sulfate ion, and propyl sulfate ion.

Squarylium dye However, in the above chemical formulas (23) and (24), A is hydrogen, a halogen atom, an alkyl group, an alkoxy group, a nitro group, a cyano group, a trifluoromethyl group, And n is an integer of 0 to 5, and when n is 2 to 5, A may be the same or different. Further, Y represents hydrogen, an alkyl group, a halogen atom or a hydroxyl group, R ₁ ,
R ₂ represents an alkyl group, a phenyl group which may have a substituent, a benzyl group which may have a substituent, or an allyl group.

However, in the above (25), X is an oxygen atom or a sulfur atom, R is an alkyl group having at least 3 carbon atoms, and R ₁ is a hydrogen atom or a methyl group.

Croconic methine dye However, in the above chemical formulas (26) and (27), R ₁ and R ₂
Is a substituted or unsubstituted alkyl group, cyclic alkyl group,
An allyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted aryl group is shown. Z ₁ and Z ₂ represent a group of non-metal atoms necessary for completing a substituted or unsubstituted heterocycle. m and n are 0 or 1. M ⁺ represents a cation X ^-
Indicates an anion.

However, in the above chemical formula (28), R ₁ and R ₂ represent an alkyl group. Further, R ₁ and R ₂ may form a ring together with the nitrogen atom. R ₃ , R ₄ , R ₅ and R ₆ are a hydrogen atom, a halogen atom,
An alkyl group, an alkoxy group or a hydroxy group is shown. R ₁ and R ₂ may combine to form a benzene ring, or R ₃ and R ₄ and R ₅ and R ₆ may combine to form a benzene ring.

Merocyanine dye However, in the above formula (29), Is Represents a ring such as Etc., and n represents 1 or 2.

The light absorbing layer 2 of the optical recording information recording medium according to the present invention
The preferable cyanine dye of the material used in (1) is a dye having a structure represented by the following general formula, in which a heterocycle is bound by a methine chain.

However, in the above chemical formula, Y and Y ′ are O, S, Se,
NH, -CH = CH-, a _{CH 3 -C-CH 3, R} , R ' is an alkyl group, X is a halogen atom, n represents a 0,1,2,3.

Specific examples thereof include indolenine-based cyanine dyes and thiazole-based cyanine dyes, including the following.

However, in the above chemical formulas (30) and (31), R ₁ , R ₂ and R ₃ may be the same or different, and each is C ₁ to
Represents an alkyl group of C ₆ , X represents halogen, perhalogen acid, tetrafluoroboric acid, toluenesulfonic acid or alkylsulfuric acid, A represents a benzene ring or a naphthyl ring, and a substituent on each ring. As alkyl,
There may or may not be alkoxy, hydroxy, carboxyl, halogen, allyl or alkylcarboxyl and n represents an integer of 0 or 1-3.

Further, an alkyl group on each carbon forming the methine chain,
A halogen atom may be substituted, and carbon atoms may be cyclically bonded with a saturated hydrocarbon.

Further, X may be a metal complex anion shown below.

However, in the above formulas (32) to (36), M is Ni, C
indicates transition metals such as o, Mn, Cu, Pd and Pt, R ₁ not R ₄
May be the same or different and each represents a substituted or unsubstituted alkyl, aryl or amino group,
R ₅ to R ₁₂ may be the same or different, each represents a hydrogen atom, a halogen atom or a substituted or unsubstituted alkyl, acyl, alkoxy, acyloxy, aryl, alkenyl or amino group, and R ₁₃ is substituted or An unsubstituted amino group is shown and is represented by l, m, n, p, q and r.
Represents 0 or 1-4, and u and v are 0 or 1-2.
Indicates.

However, the present invention is not limited to the above cyanine dyes, as long as it is a light-absorbing cyanine dye, other cyanine dyes, for example, quinoline cyanine dyes, oxazole cyanine dyes and other cyanine dyes Also,
It is possible to obtain the effects of the present invention.

Indodicarbocyanine, which is a more desirable cyanine dye for obtaining the effects of the present invention, is represented by the following formula.

However, A and A ′ are an atomic group forming a benzene ring or a substituted benzene ring or forming a naphthalene ring or a substituted naphthalene ring, and may be the same or different. B is pentamethine (-CH = CH-CH =
CH-CH =), and each hydrogen atom may be substituted with a halogen atom, an alkyl group, an alkoxy group, a gefnylamino group, or the like, and has a substituted or unsubstituted cyclic side chain extending over a plurality of carbon atoms. You may.

R ₁ and R ₁ ′ are a substituted or unsubstituted alkyl group, alkoxy group, alkylhydroxy group, aralkyl group, alkenyl group, alkylcarboxyl group, alkylsulfonyl group or an alkylcarboxyl group bonded to an alkali metal ion or an alkyl group, or It is an alkylsulfonyl group and may be the same or different.

X ₁ ^- represents a halogen atom, perchloric acid, borofluoride hydrochloric acid, benzenesulfonic acid, toluenesulfonic acid, alkylsulfonic acid, benzenesulfonic acid, an anion such as an alkyl carboxylic acid or trifluoromethyl carboxylic acid, When R ₁ and R ₁ ′ have a group to which an alkali metal ion is bonded, X ₁ ⁻ may not be present.

Substituents A and A'of the cyanine dye represented by the above general formula
Include a substituted or unsubstituted benzene ring or a substituted or unsubstituted naphthalene ring, and these substituents include an alkyl group, an alkoxy group, a hydroxy group, a carboxyl group, a halogen atom, an allyl group and an alkylcarboxyl group. , An alkylalkoxy group, an aralkyl group, an alkylcarbonyl group, a sulfonate alkyl group bonded to a metal ion, a nitro group, an amino group, an alkylamino group, an aryl group, a phenylethylene group, and the following.

_{-CH = CH-CN, -NHCOCH 3} , Further, a combination of a plurality of indolenine type cyanines having each of these substituents can also be used. For example, as the substituents attached to the substituents A and A ′ of those substances, those shown in Table 1 can be exemplified.

One of the two types of cyanine may be a cyanine other than indodicarbocyanine.

The cyclic side chain bonded to B in the above general formula is a carbon bonded to a plurality of carbons of a pentamethine chain, for example, between the second and fourth carbons to form, for example, a 4-membered ring, a 5-membered ring, a 6-membered ring, etc. A bonding chain composed of the above atoms may be mentioned, which may have a substituent. The substituent directly bonded to B or on the above cyclic side chain includes a halogen atom, a diphenylamino group, an alkoxy group (eg, a lower alkoxy group such as methoxy and ethoxy), an alkyl group (eg, a lower alkyl group such as methyl and ethyl). ) Etc.

In addition to the organic dye and the cyanine dye, the light absorbing layer may contain other dye, resin (for example, thermoplastic resin such as nitrocellulose, thermoplastic elastomer), liquid rubber, or the like. Specifically, in addition to those listed in the examples below, as the thermoplastic resin, isobutylene, maleic anhydride copolymer, ethylene vinyl acetate copolymer, carboxyvinyl polymer, chlorinated polypropylene, polyethylene oxide, polyamide (nylon 6 ,
Nylon 12, methoxymethylated polyamide, etc.), coumarone resin, ketone resin, vinyl acetate, polystyrene, PVA
(Polyvinyl alcohol), PVE (polyvinyl ester), etc., cellulose derivatives include carboxymethyl cellulose, nitrocellulose, HPC (hydroxypropyl cellulose), HEC (hydroxyethyl cellulose), MC (methyl cellulose), EC (ethyl cellulose), EHEC (ethyl cellulose). Hydroxyethyl cellulose), CM
Examples include EC (carboxymethyl ethyl cellulose) and the like, oligomers such as oligostyrene and methylstyrene oligomer, and elastomers and rubbers such as styrene block copolymers and urethane-based thermoplastic elastomers.

The light absorption layer 2 is formed by first coating the surface of the substrate 1 with the cyanine dye dissolved in an organic solvent such as acetylacetone, methyl cellosolve, or toluene. Examples of means for this include vapor deposition method, LB method, spin coating method, and the like, and the film thickness of the light absorption layer 2 can be controlled by adjusting the concentration, viscosity, and drying rate of the solvent of the coating material. Therefore, the spin coating method is preferable.

As the organic solvent, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, amyl alcohol, isoamyl alcohol, hexyl alcohol, heptanol, benzyl alcohol, cyclohexanol, furfuryl alcohol, cellosolve, diethyl cellosolve, butyl cellosolve, Ethers such as methyl carbitol, carbitol, acetal, dioxane and tetrahydrofuran,
Acetone, methyl ethyl ketone, methyl isobutyl ketone, diacetone alcohol, cyclohexanone, acetophenone, and other ketones, ethyl formate, butyl formate, amyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, phenyl acetate, methyl cellosolve acetate , Esters such as cellosolve acetate, nitrohydrocarbons such as nitromethane, nitroethane, nitropropane, nitrobutanol, nitrobenzene, methyl chloride, methylene chloride, chloroform, methyl bromide, promoform, methylene iodide, ethyl chloride, ethylene chloride, Ethylidene chloride, trichloroethane, trichloroethylene, propylene chloride, butyl chloride, dichlorobutane, hexachloropropylene, dichloropentane, amyl chloride, chlorben Chlorinated solvents such as benzene, 0-dichlorobenzene, trichlorobenzene, chlorotoluene, dichlorotoluene, etc., other paraldehyde, crotonaldehyde, furfural, aldol, acetonitrile, formamide, dimethylformamide, acetol, γ-valerolactone, amylphenol, Sulfolane, 2-mercaptoethyl alcohol, dimethyl sulfoxide, N
Solvents such as methylpyrrolidone and methyl carbamate may also be used. Further, these organic solvents may be solvated with the cyanine dye and contained in the light absorption layer.

The reflection layer 3 is a metal film, and is formed of, for example, gold, silver, copper, aluminum, or an alloy containing these by a method such as a vapor deposition method or a sputtering method. Among these, a metal film mainly composed of gold or an alloy containing gold is preferable because it is necessary to have a reflectance of 70% or more.

The protective layer 4 is formed of a resin having excellent impact resistance similar to that of the translucent substrate 1, and is formed by applying an ultraviolet curable resin by a spin coating method and irradiating the ultraviolet ray to cure the resin. In addition, epoxy resin, acrylic resin, silicone hard coat resin, etc. are used.
It may be formed of an elastic material such as urethane resin in order to provide a cushioning effect.

Further, in the optical information recording medium according to the present invention, a layer on the back side of the light absorption layer 2 with respect to the transparent substrate 1, for example, the light reflection layer 3 or the protective layer 4 is used as the layer in which the pits 5 are formed. In comparison, it is desirable to use a material having a high heat distortion temperature and a high hardness. Forming the layer on the back side with a layer of high hardness is effective in reducing the block error rate of the recording signal.

An oxidation resistant layer that prevents oxidation of the reflective layer 3 may be interposed between the reflective layer 3 and the protective layer 4.

More specific examples of the present invention will be described below.

Example 1 A spiral pregroup having a width of 0.8 μm, a depth of 0.08 μm, and a pitch of 1.6 μm, formed with a thickness of 1.2 mm and an outer diameter of 120 mm.
A polycarbonate substrate 1 having φ and an inner diameter of 15 mmφ was molded by an injection molding method.

0.95 g of 1,1′-dibutyl 3,3,3 ′ as a cyanine dye,
3'Tetramethyl 4,5,4 ', 5'-dibenzoindodicarbocyanine perchlorate (manufactured by Nippon Photosensitive Dyes Co., Ltd., product number
NK3219) was dissolved in 10 ml of an acetylacetone solvent, and this was coated on the above substrate 1 by a spin coating method to form a light absorption layer 2 having a film thickness of 250 nm. The complex refractive index of the light absorption layer 2 is n _abs = 2.7 and k _abs = 0.05. As will be described later, the wavelength of the semiconductor laser for reproducing light is λ = 780 nm, and ρ = n _abs d _abs /λ=0.87.

A 60 nm-thick film was formed on the entire surface of this disk by vacuum deposition.
An Au film was formed and a light reflection layer 3 was formed. Further, an ultraviolet curable resin is spin-coated on the light reflecting layer 3 and is irradiated with ultraviolet rays to be cured to form a protective layer 4 having a thickness of 10 μm.
Was formed.

The optical disc thus obtained was irradiated with a semiconductor laser having a wavelength of 780 nm at a linear velocity of 1.2 m / sec and a recording power of 6.8 mW, and EFM was applied.
The signal was recorded. Then, use this optical disc as a commercially available CD
When reproduced with a player (Aurex XR-V73, reproduction light has wavelength λ = 780 nm, reproduction power of 0.5 mW laser), optical disk reflectance is 70.2%, I ₁₁ / I _top obtained from the eye pattern of the reproduction signal is 0.9. , I ₃ / I _top was 0.6, and the block error rate was 2.0 × 10 ^-3 .

According to the CD standard, the reflectance is 70% or more, I ₁₁ / I _top is 0.6 or more, I ₃ / I _top is 0.3 to 0.7, and the block error rate is 3.0 × 1
0 ^-2 are determined in the following, an optical disc according to this embodiment is to satisfy this standard.

(Example) A polycarbonate substrate 1 molded in the same manner as in Example 1 above was coated with 1.45 g of the same cyanine dye as in Example 1 dissolved in 10 cc of an acetylacetone solvent by spin coating to give a film having a thickness of 410 nm. The light absorption layer 2 was formed. In this case, ρ = n _abs d _abs /λ=1.42.

A light reflecting layer 3 was formed on the entire surface of this disc in the same manner as in Example 1 above. Further, an ultraviolet curable resin was spin-coated on the light reflecting layer 3 and was irradiated with ultraviolet rays to be cured to form a protective layer 4 having a thickness of 10 μm.

An EFM signal was recorded on the optical disc thus obtained in the same manner as in Example 1 above. When this optical disk was reproduced by the same CD player as used in Example 1, the optical disk had a reflectance of 72%, I ₁₁ / I _top or 0.9.
5, I ₃ / I _top 0.70, block error rate 6.0 × 10 ^-3
Met. Therefore, the optical disc according to this embodiment also satisfies the CD standard as in the above-mentioned embodiment.

[Effects of the Invention] As described above, according to the present invention, a reproduction signal having a high reflectance of 70% or more and a high degree of modulation can be obtained, and thus, an optical information that can obtain an output signal conforming to the CD standard. A recording medium is obtained.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of the structure of an optical information recording medium, FIG. 2 is a partially enlarged view taken along the track before optical recording in FIG. 1, and FIG. FIG. 1 is a partially enlarged view of a section taken along the track after the optical recording in FIG. 1, and FIG. 4 is a real part n _abs of the complex refractive index of the light absorption layer of the optical disk and a film thickness d.
_abs and reproduction light wavelength λ = ρ = n _abs d _abs / λ
5 is a graph showing an example of the relationship between the value of and the reflectance of laser light, and FIG. 5 is an imaginary part k _abs of the complex refractive index of the light absorption layer of the optical disc
3 is a graph showing the relationship between the value of and the reflectance of laser light. 1 ... Substrate, 2 ... Light absorbing layer, 3 ... Light reflecting layer, 4 ...
Protective layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takashi Ishiguro 6-16-20 Ueno, Taito-ku, Tokyo Within Taiyo Denki Co., Ltd.

Claims (3)

[Claims] 1. A light-absorbing layer containing a light-absorbing dye is provided directly or through another layer on a light-transmitting substrate, and directly or through another layer on the light-absorbing layer. In an optical information recording medium provided with a light reflection layer made of a metal film, ρ = n _abs d _abs given by the real part n _abs of the complex refractive index of the light absorption layer, the film thickness d _abs, and the wavelength λ of the reproduction light. / Λ is 0.6 <ρ <1.6
And the imaginary part _Kabs of the complex index of the light absorption layer is _Kabs <
An optical information recording medium characterized by being 0.2. 2. An optical information recording medium according to claim 1, wherein the light absorbing layer is a cyanine dye. 3. An optical information recording medium according to claim 2, wherein the cyanine dye forming the light absorbing layer is a compound represented by the following general formula. (However, A and A ′ are atomic groups that form a benzene ring or a substituted benzene ring, or form a naphthalene ring or a substituted naphthalene ring, and may be the same or different. B is Pentamethine (-CH = CH-CH = CH-CH =), each hydrogen atom may be substituted with a halogen atom, an alkyl group, an alkoxy group, a diphenylamino group, or the like, or a substitution between a plurality of carbon atoms or R ₁ and R ₁ ′ may have an unsubstituted cyclic side chain, and R ₁ and R ₁ ′ each represent a substituted or unsubstituted alkyl group, alkoxy group, alkylhydroxy group, aralkyl group, alkenyl group, alkylcarboxyl group, alkylsulfonyl group or an alkylcarboxyl group or alkylsulfonyl group bonded with an alkali metal ion or an alkyl group, may be the same or different X ₁ ^-. the It represents a halogen atom, perchloric acid, borofluoride hydrochloric acid, benzenesulfonic acid, toluenesulfonic acid, alkylsulfonic acid, benzenesulfonic acid, an anion such as an alkyl carboxylic acid or trifluoromethyl carboxylic acid,
When R ₁ and R ₁ ′ have a group to which an alkali metal ion is bonded, X ₁ ⁻ may not be present. )